I think with tools like this, that's a very common reaction. My suggestion to the founders would be to work to leverage that sentiment to get RentPost in front of landlords. A couple ideas:
* Allow roommates to collectively pay their rent online without the landlord being a customer of RentPost. You then turn around and cut a cheque which is mailed to the landlord. Included with the cheque is the upsell to subscribe to the service.
* Allow tenants to submit maintenance requests, etc, turn these into an email to the landlord. The property manager could simply reply to the email, but you could also give them the option to manage the "ticket" online & you could ease them into your service.
On a different note, hit up the Property Management trade shows!